This invention is directed to the method of improving the transverse, i.e. edge-to-edge, properties of a hot strip mill product, by subjecting such product to a quenching system which generates a continuous curtain of quenchant, where the quenchant is recycled industrial water. While the method of this invention will be applicable to many types of water systems, it is particularly important in this age of conservation and ecological concern to have such a method which can effectively use recycled industrial water and produce the results to be described hereinafter.
Hot strip mills, as are known today, have emerged from simple reversing hand mills to the present time with synchronized tandem mills of from five to seven in number. After the final finishing stand, the most down stream of said tandem mills, the hot strip, moving at a rapid pace, traverses a run-out table to be coiled at the end thereof. To develop desirable metallurgical properties, and to facilitate coiling and handling, it is necessary to apply quenchant, typically in the form of water, to the hot moving strip on the run out table. Since cooling or quenching is a significant property modifying step, it is important that such cooling or quenching be as uniform as possible.
Different methods or systems have been used over the years to quench the hot strip. To use industrial waters, which could readily clog nozzles or spray systems, a water overflow curtain system was developed. Such system is a water box having a pair of stainless steel throat plates projecting therefrom between which such industrial water flows onto the hot strip. With such water the system was only marginally successful.
It will be recalled that if the water supplied to the curtain system is mill recycled industrial water from a scale pit, for example, problems can occur. This water contains a heavy concentration of suspended solids, oils, and varying sizes of mill scale. When this type of water passes between the stainless steel throat plates, several things may happen, namely:
1. the scale etches the highly polished stainless steel plates, PA1 2. the suspended particles adhere to the surface causing the water to split as it passes these deposits, and PA1 3. the oil veins on the smooth steel surface causes the water to track in the grooves, thus producing more splits.
The net effect of the above is a discontinuous curtain of water impacting against the hot strip. This results in variations in cooling rates and non-uniform properties from edge-to-edge, as well as strip end-to-end, and through the thickness of the strip. These problems may be compounded by the fact that for a given order, one or more pairs of throat plates may not be used. As a result, the industrial water contaminants adhering to the plate surfaces harden to produce new sources of problems during subsequent use.
The method of this invention is based on the recognition of the source of the problem and the means to overcome such problem. The answer, and the repeatability of results from such method, will become apparent from the specification which follows.